US 7810400 B2
A method for determining one or more fluid flow parameters for a fluid flowing within a pipe is provided. The fluid is a mixture of solid particles and gas. The method includes the steps of: a) providing a meter operable to determine the velocity of the fluid flow through the pipe, which meter is substantially insensitive to the particulate/gas mass ratio of the fluid flow; b) determining the velocity of the fluid flow within the pipe using the meter; and c) determining a particulate/gas mass ratio using a density value for the gas within the flow and the determined fluid flow velocity.
1. A method for determining one or more fluid flow parameters for a fluid flow within a pipe, the fluid flow comprising a mixture of solid particles and gas, the method comprising:
receiving signals indicative of unsteady pressure variations within the pipe, the signals being generated by a flow meter that is substantially insensitive to a particulate/gas mass ratio of the fluid flow;
determining the velocity of the fluid flow based at least partly on the unsteady pressure variations sensed by the flow meter; and
determining the particulate/gas mass ratio of the fluid flow based at least partly on a density value for the gas within the fluid flow and the velocity determined for the determined fluid flow.
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15. A method for determining one or more fluid flow parameters of a fluid flow within a pipe, the fluid flow comprising a mixture of solid particles and gas, the method comprising the steps of:
sensing the fluid flow for unsteady pressures generated by pressure disturbances convecting with the fluid flow using a flow meter that is substantially insensitive to a particulate/pas mass ratio of the fluid flow, and creating signals indicative of the unsteady pressures generated by the pressure disturbances;
determining the velocity of the fluid flow within the pipe using the signals indicative of the unsteady pressures; and
determining the particulate/gas mass ratio using a density value for the gas within the fluid flow and the velocity determined for the fluid flow.
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This application claims the benefit of U.S. Provisional Patent Application No. 60/961,721 filed Jul. 24, 2007, U.S. Provisional Patent Application No. 61/027,500 filed Feb. 11, 2008, and U.S. Provisional Patent Application No. 61/034,602 filed Mar. 7, 2008, all of which are incorporated by reference herein in their entirety.
This invention provides a method to measure parameters of a fluid/particle mixture in a pipe that can be used in many applications, such as in chemical, pharmaceutical, petroleum and power generation. In particular, the invention provides a method to measure pulverized coal and air mixtures used in pulverized fuel delivery systems found within a large percentage of coal fired boilers used in the power generation industry.
Currently, well over 50% of the electricity in the U.S. is generated with coal. While coal is considered a cost effective, abundant resource in the U.S., the use of coal has been restricted due in large part to environmental concerns. To mitigate this impact, the U.S. Department of Energy and the power generation industry have large programs designed to develop technology to reduce the environment effects of burning coal. These Clean Coal Initiatives include technology designed to develop improvements in the combustion process to improve efficiency while reducing pollutants such as unburned carbon, ash, and nitrous oxide (N2O).
The ability to measure the flow rate and composition of the air/coal mixture within the coal pipes is an important performance aspect of any particle fuel delivery system. The industry recognizes this and therefore has been developing a wide variety of technologies to perform these measurements. The technologies include probe devices and sampling devices, as well as real time meters based on a wide variety of technologies including electrostatic charges, microwaves, and ultrasonic. Many of these devices suffer from complexity, require substantial maintenance, impede flow, or are unreliable. A sensing device that is accurate, non-intrusive, and reliable would be highly advantageous.
According to the present invention, a method for determining one or more fluid flow parameters for a fluid flowing within a pipe is provided. The fluid comprises a mixture of solid particles and gas. The method comprises the steps of: a) providing a meter operable to determine the velocity of the fluid flow through the pipe, which meter is substantially insensitive to the particulate/gas mass ratio of the fluid flow; b) determining the velocity of the fluid flow within the pipe using the meter; and c) determining a particulate/gas mass ratio using a density value for the gas within the flow and the determined fluid flow velocity.
One of the advantages of the present invention method is that it provides a simple, non-intrusive method for determining the particulate/gas mass ratio of a fluid flow that is accurate regardless of the particulate loading within the fluid flow. The method determines the velocity of the fluid flow using sensors that are insensitive to the presence of particles within the fluid flow. The velocity, in turn, is used to determine the particulate/gas mass ratio, and can be used to determine the particulate mass flow rate and the gas mass flow rate. Consequently, accurate flow data is provided regardless of the particulate/gas mass ratio of the fluid flow.
Other advantages include the fact that the present method does not require external inputs. For example, in the context of a coal/air delivery system, the present invention does not require the input of the pulverizer feed rate. Because the parameters determined using the present invention method are independent of the pulverizer feed rate, the same parameters can be used to detect anomalies in the feed rate. Another advantage is that the method can be performed independent of upstream pipe geometry and control components. Consequently, the present method can be operated in a closed loop fashion. Still another advantage is that the method can be applied to a single pipe or a plurality of pipes within a system, as is diagrammatically depicted in
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.
The apparatus includes an at least one flow meter 116 having an array of sensors 118 (sonar based flow meter; see
Each DP meter 114 is used to determine the difference in pressure within the flow 104 between at least two points in the pipe, or pipe system. In the system shown in
Now referring to
Although the sonar based flow meter 116 is diagrammatically shown in
As indicated above, the signals P1(t) . . . PN(t) provided by the pressure sensors 118 of each array 132 may be processed by a signal processor 134 dedicated to that array, or may be processed collectively by a common processing unit 120. Each signal processor 134 may, for example, be a microprocessor and the processing unit 120 may be a personal computer or other general purpose computer. It is contemplated that the signal processors 134 may be analog or digital signal processing devices for executing programmed instructions, such as one or more microprocessors or application specific integrated circuits (ASICS), and may include memory for storing programmed instructions, set points, parameters, and for buffering or otherwise storing data. Further, it should be appreciated that some or all of the functions within the flow logic 136 may be implemented in software (using a microprocessor or computer) and/or firmware, or may be implemented using analog and/or digital hardware, having sufficient memory, interfaces, and capacity to perform the functions described herein.
The processing unit 120, in response to the flow velocity provided by the sonar based flow meter(s) 116 (and in some embodiments, the ΔP provided by the DP meter 114) is operable to determine flow parameters such as the particulate/air mass ratio, the mass flow rate of the gas portion, and the mass flow rate of the particulate portion of the particulate/gas flow within each pipe sensed, utilizing the flow logic 136. The processing unit 120 may output the determined flow parameter to a display 140, another input/output (I/O) device 142, or another processing device for further processing. Moreover, the I/O device 142 may also accept user input parameters as may be necessary for the flow logic 136. The I/O device 142, display 140, and/or signal processor 134 unit may be mounted in a common housing, which may be attached to the array 132 by a flexible cable, wireless connection, or the like.
It is also contemplated that signals from the DP meter 114 may be provided to the signal processor 134 of the respective sonar based flow meter 116, and the signal processor 134 may determine the desired parameters; e.g., particulate/gas mass ratio, the gas mass flow rate, and the particulate mass flow rate. Conversely, signals from the sonar based flow meter 116 may be provided to the signal processor 130 of the respective DP meter 114, and the signal processor 130 may determine the desired parameters (e.g., particulate/gas mass ratio, the gas mass flow rate, and the particulate mass flow rate).
In various embodiments of the present invention, a piezoelectronic pressure transducer may be used as one or more of the pressure sensors 118 and it may measure the unsteady (or dynamic or ac) pressure variations inside the pipe 124 by measuring the pressure levels inside the pipe 124. For example, the sensors 118 may comprise pressure sensors manufactured by PCB Piezotronics of Depew, N.Y. The pressure sensors may include integrated circuit piezoelectric voltage mode-type sensors that feature built-in microelectronic amplifiers, and convert the high-impedance charge into a low-impedance voltage output. Specifically, a Model 106B manufactured by PCB Piezotronics can be used, which sensor is a high sensitivity, acceleration compensated integrated circuit piezoelectric quartz pressure sensor suitable for measuring low pressure acoustic phenomena in hydraulic and pneumatic systems. It has the capability to measure small pressure changes of less than 0.001 psi under high static conditions. The 106B has a sensitivity of 300 mV/psi and a resolution of 91 dB (0.0001 psi). The sensors 118 may incorporate a built-in MOSFET microelectronic amplifier to convert the high-impedance charge output into a low-impedance voltage signal. The sensors 118 may be powered from a constant-current source and can operate over long coaxial or ribbon cable without signal degradation.
Acceptable piezoelectric sensors may include a piezoelectric material (e.g., polymer, polarized fluoropolymer—PVDF, co-polymer films, flexible PZR sensors, etc.) that measures strain induced within the process pipe 124 due to unsteady pressure variations within the flow 104. Strain within the pipe 124 is transduced to an output voltage or current by the attached piezoelectric sensors 118. The piezoelectric material may be adhered to the outer surface of a steel strap that extends around and clamps onto the outer surface of the pipe 124. The piezoelectric sensing element is typically conformal to allow complete or nearly complete circumferential measurement of induced strain. Advantages of sensing with piezoelectric films include non-intrusive flow rate measurements, low cost, no excitation source required, easily mountable in a variety of configurations to enhance signal detection schemes (e.g., co-located sensors, segmented sensors with opposing polarity configurations, wide sensors to enhance acoustic signal detection and minimize vortical noise detection, tailored sensor geometries to minimize sensitivity to pipe modes, and differencing of sensors to eliminate acoustic noise from vortical signals), and piezoelectric films can be constructed to be operable in higher temperature environments (e.g., 140 C).
The present invention contemplates that the above-described sonar based flow meter 116 may be substituted with an ultrasonic flow meter similar to any one of the following types of meters: Transit Time Ultrasonic Flow Meter (TTUF), Doppler Ultrasonic Flowmeter (DUF), and Cross Correlation Ultrasonic Flow Meter (CCUF), similar to that described in the article “Guidelines for the Use of Ultrasonic Non-Invasive Metering Techniques” by M. L. Sanderson and H. Yeung, published on Jul. 17, 2002, which is incorporated herein by reference. An acceptable CCUF is a GE Panametrics DigitalFlow™ CTF878 flowmeter, which has a pair of ultrasonic sensors that can be disposed axially along the pipe.
Flow Logic—Velocity Processing:
The signal processor 134 includes data acquisition unit 148 (e.g., A/D converter; see
The data accumulator 152 accumulates the frequency signals P1(ω) . . . PN(ω) over a sampling interval, and provides the data to an array processor 156, which performs a spatial-temporal (two-dimensional) transform of the sensor data, from the xt domain to the k-ω domain, and then calculates the power in the k-ω domain, as represented by the k-ω plot shown in
It should be appreciated that the prior art teaches many algorithms for use in spatially and temporally decomposing a signal from a phased array of sensors, and the present invention is not restricted to any particular algorithm. Acceptable adaptive array processing algorithms include the Capon method/algorithm and the MUSIC algorithm. The present invention recognizes that such techniques can be used to determine flow velocity; i.e., that the signals caused by a stochastic parameter convecting with a flow are time stationary and have a coherence length long enough that it is practical to locate sensor units apart from each other and yet still be within the coherence length. Convective characteristics or parameters have a dispersion relationship that can be approximated by the straight-line equation, k=ω/μ where μ is the convection velocity (flow velocity). A plot of k-ω pairs obtained from a spectral analysis of sensor samples associated with convective parameters portrayed so that the energy of the disturbance spectrally corresponding to pairings that might be described as a substantially straight ridge, a ridge that in turbulent boundary layer theory is called a convective ridge. What is being sensed is not a plurality of discrete events of turbulent eddies, but rather a continuum of possibly overlapping events forming a temporally stationary, essentially white process over the frequency range of interest. In other words, the convective eddies 146 are distributed over a range of length scales and hence temporal frequencies.
To calculate the power in the k-ω plane, as represented by a k-ω plot (see
Once the power in the k-ω plane is determined, a convective ridge identifier 158 uses one or another feature extraction method to determine the location and orientation (slope) of any convective ridge 154 present in the k-ω plane. In one embodiment, a so-called slant stacking method is used, a method in which the accumulated frequency of k-ω pairs in the k-ω plot along different rays emanating from the origin are compared, each different ray being associated with a different trial convection velocity. The velocity of the flow 104 can be determined from the slope of the rays.
In a piping system 106 such as that shown in
In a first embodiment, for example, the pressure loss through a section of pipe within the coal/air piping system 106 shown in
A mean pressure loss coefficient can be defined using the following equation:
Now referring to
For a given piping system for a particulate/gas mixture, the pressure loss through a section of pipe may be described as a function of the elevation change (h), the bulk velocity of the flow mixture (u), the mixture density (ρ), and a pressure loss coefficient (K). The pressure loss can be expressed as follows:
The pressure loss coefficient K may be determined through in situ calibration. If the flow 104 running through the pipe 124 contains only air, the pressure loss coefficient through the pipe will be a function of only the pipe geometry (e.g., the number of elbows, straight run length, wall roughness, etc.) For coal/air mixtures, the pressure loss coefficient K will also be dependent on the piping geometry, but may be a function of the coal/air ratio as well. It can be assumed that the pressure loss coefficient is linear with the coal/air ratio:
Once the CAR value for each feed pipe 124 is determined, the mass flow rates can be determined using the following relationships:
Now referring to
For a particulate/gas mixture flowing through a given pipe length (e.g., one like that shown in
As stated above, for those applications where the volume fraction of the particulate component is much less than the volume fraction of the gas component (e.g., φCOAL<<φAIR), the density of the flow may also be expressed as is disclosed in Eqn. 9. With the determined value of the flow density and a known value of the air density (at a given temperature), an initial value for the CAR for each feed pipe can be determined using Eqn. 9. Once the CAR value for each feed pipe is determined, the mass flow rates can be determined using Eqns. 12 and 13.
While the invention disclosed herein is discussed in terms of one or more DP meters 114 and one or more sonar meters 116, the present invention contemplates that any meter and/or combination of meters suitable to the desired end purpose may be used, such that the meters provide an output measurement having a repeatable over report function (or output signal) with respect to the particulate/gas mass ratio of the flow 104, wherein the over reporting is substantially less than the over reporting of the DP meter 114. The greater the difference in the over reporting between the meter and the DP meter 114, the greater the accuracy and resolution of the particulate/gas mass ratio measurement. Moreover, one should appreciate that the meters (e.g., sonar and/or ultrasonic) combined with the differential meter may also comprise non-invasive clamp on sensors or wetted sensors.
The method of the invention may be embodied in the form of a computer or controller implemented processes. The invention may also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, and/or any other computer-readable medium, wherein when the computer program code is loaded into and executed by a computer or controller, the computer or controller becomes an apparatus for practicing the invention. The invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein when the computer program code is loaded into and executed by a computer or a controller, the computer or controller becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor the computer program code segments may configure the microprocessor to create specific logic circuits.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, may modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed herein as the best mode contemplated for carrying out this invention.